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SECTOR FOCUS: INDUSTRIAL


Biodegradable hydraulic fluids: Do they have a bright future?


Dr. Raj Shah, Director, Koehler Instrument Company, Dr. Mathias Woydt, Managing Director, MATRILUB Materials Tribology Lubrication, and Ms. Amanda Loo and Mr. Stanley Zhang, Stony Brook University


Hydraulic fluids are used in various applications and environments. They represent a powerful mechanical solution for actuation over electrical actuators and have a market share between 8-10% of the total lubricant tonnages. The market for base oils is dominated by the Group I category, which accounts for about 52% of the total base oil market by volume, with the overall market being valued at approximately 25 billion USD as of 2019. Base oils find applications as motor oils, process oils, hydraulic oils, and industrial oils, with the automotive sector, in particular, accounting for 44% of the 2019 base oil market [1]. Hydraulic equipment requires fluids that are most efficient in a certain range of temperature, pressure, or viscosity.


Effects of Hydraulic Fluids on the Environment Hydraulic equipment is often exposed to nature and water. Tube bursts and inevitable leakages spill into the environment, which accounts for a significant loss of the fill per year. The introduction of lubricating oils into natural bodies of water can cause significant environmental detriment and degrade water quality. The presence of oil on water surfaces raises considerable environmental concerns, as polluted waters experience decreases in natural oxygen transfer. The development of more environmentally friendly hydraulic fluids is integral to limiting environmental detriment and promoting sustainable tribology [1].


Evolution of Biodegradable Hydraulic Fluids In 1988, the accumulation of non-degradable lubricants and engine oils from motorboats formed thick sediments at the bottom of Lake Constance, a water reservoir serving around 10 million people in Germany, Switzerland, and Austria. This occurrence


16 LUBE MAGAZINE NO.165 OCTOBER 2021


highlighted the potentially disastrous effects of petroleum-based and synthetic lubricants, leading to the development of biodegradable lubricants to lessen environmental impact.


The German government’s ecolabel, “Blue Angel,” was introduced in 1978 and was awarded to products that are deemed environmentally friendly. The first ecolabels that specified the biodegradable criteria for saw chain oils (RAL UZ-48), mold release agents (RAL UZ-64), and hydraulic oils (RAL UZ-79) were released in 1988, 1991, and 1996, respectively. By 2010, these three ecolabels were formally merged into a single ecolabel, known as, “RAL UZ-178.”


In 1994, the German Association of Mechanical Engineering Industry (VDMA) detailed the minimum technical criteria for environmentally acceptable hydraulic fluids with VDMA 24568. These requirements would later be antiquated by the introduction of ISO 15380 in 2002. In December 1996, the American Society for Testing and Materials (ASTM) published D6046, which established categories of hydraulic fluids based on environmental responses. ASTM would later go on to publish D6006 in October 1997, which assessed the biodegradability of unused fully formulated hydraulic fluids.


During the early days of bio-lubricants, the characteristic of biodegradability was erroneously interpreted by agricultural ministries around the world to only encompass vegetable sources, such as soybean, rapeseed, and sunflower. However, the thermo-oxidative stability of vegetable oils is limited due to the existence of double bonds in their molecular backbones. In addition, the prohibitively high costs of esters further contributed to tarnish the reputation


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